diff options
Diffstat (limited to 'doc/src/sgml/ref/alter_table.sgml')
| -rw-r--r-- | doc/src/sgml/ref/alter_table.sgml | 25 |
1 files changed, 13 insertions, 12 deletions
diff --git a/doc/src/sgml/ref/alter_table.sgml b/doc/src/sgml/ref/alter_table.sgml index d63f3a621ac..541e093a519 100644 --- a/doc/src/sgml/ref/alter_table.sgml +++ b/doc/src/sgml/ref/alter_table.sgml @@ -240,9 +240,10 @@ WITH ( MODULUS <replaceable class="parameter">numeric_literal</replaceable>, REM provided none of the records in the table contain a <literal>NULL</literal> value for the column. Ordinarily this is checked during the <literal>ALTER TABLE</literal> by scanning the - entire table; however, if a valid <literal>CHECK</literal> constraint is - found which proves no <literal>NULL</literal> can exist, then the - table scan is skipped. + entire table, unless <literal>NOT VALID</literal> is specified; + however, if a valid <literal>CHECK</literal> constraint exists + (and is not dropped in the same command) which proves no + <literal>NULL</literal> can exist, then the table scan is skipped. If a column has an invalid not-null constraint, <literal>SET NOT NULL</literal> validates it. </para> @@ -460,8 +461,8 @@ WITH ( MODULUS <replaceable class="parameter">numeric_literal</replaceable>, REM <para> This form adds a new constraint to a table using the same constraint syntax as <link linkend="sql-createtable"><command>CREATE TABLE</command></link>, plus the option <literal>NOT - VALID</literal>, which is currently only allowed for foreign key, - <literal>CHECK</literal> constraints and not-null constraints. + VALID</literal>, which is currently only allowed for foreign-key, + <literal>CHECK</literal>, and not-null constraints. </para> <para> @@ -469,7 +470,7 @@ WITH ( MODULUS <replaceable class="parameter">numeric_literal</replaceable>, REM existing rows in the table satisfy the new constraint. But if the <literal>NOT VALID</literal> option is used, this potentially-lengthy scan is skipped. The constraint will still be - enforced against subsequent inserts or updates (that is, they'll fail + applied against subsequent inserts or updates (that is, they'll fail unless there is a matching row in the referenced table, in the case of foreign keys, or they'll fail unless the new row matches the specified check condition). But the @@ -591,7 +592,7 @@ WITH ( MODULUS <replaceable class="parameter">numeric_literal</replaceable>, REM This form validates a foreign key, check, or not-null constraint that was previously created as <literal>NOT VALID</literal>, by scanning the table to ensure there are no rows for which the constraint is not - satisfied. If the constraint is not enforced, an error is thrown. + satisfied. If the constraint was set to <literal>NOT ENFORCED</literal>, an error is thrown. Nothing happens if the constraint is already marked valid. (See <xref linkend="sql-altertable-notes"/> below for an explanation of the usefulness of this command.) @@ -852,7 +853,7 @@ WITH ( MODULUS <replaceable class="parameter">numeric_literal</replaceable>, REM <para> <literal>SHARE UPDATE EXCLUSIVE</literal> lock will be taken for - fillfactor, toast and autovacuum storage parameters, as well as the + fillfactor, TOAST and autovacuum storage parameters, as well as the planner parameter <varname>parallel_workers</varname>. </para> </listitem> @@ -1466,11 +1467,11 @@ WITH ( MODULUS <replaceable class="parameter">numeric_literal</replaceable>, REM </para> <para> - Adding an enforced <literal>CHECK</literal> or <literal>NOT NULL</literal> + Adding a <literal>CHECK</literal> or <literal>NOT NULL</literal> constraint requires scanning the table to verify that existing rows meet the constraint, but does not require a table rewrite. If a <literal>CHECK</literal> - constraint is added as <literal>NOT ENFORCED</literal>, the validation will - not be performed. + constraint is added as <literal>NOT ENFORCED</literal>, no verification will + be performed. </para> <para> @@ -1485,7 +1486,7 @@ WITH ( MODULUS <replaceable class="parameter">numeric_literal</replaceable>, REM </para> <para> - Scanning a large table to verify a new foreign key or check constraint + Scanning a large table to verify new foreign-key, check, or not-null constraints can take a long time, and other updates to the table are locked out until the <command>ALTER TABLE ADD CONSTRAINT</command> command is committed. The main purpose of the <literal>NOT VALID</literal> |